This invention relates to a multi-channel electromagnetic radiation transmission system and particularly to a system which is adapted to be used in a plurality of modes for the selective determination of two or more substances in a medium. More particularly, the invention relates to a system involving a series of radiation-transmissible junctions of optical fibers, which system provides substantially unattenuated output radiation signals.
The invention is also concerned with a method for the determination of two or more parameters each of which is a function of the output radiation of a radiation sensitive component, utilizing said system.
The measurement of desired parameters in various media, particularly in biological systems, is frequently required. For example, the measurement in blood of pH levels and concentration of gases, particularly oxygen and carbon dioxide, is important during surgical procedures, post-operatively, and during hospitalization under intensive care and many devices for the measurement of said physiological parameters have been suggested in the art.
U.S. Pat. No. 4,003,707, Lubbers et al, and its reissue U.S. Pat. Re. No. 31,879, disclose a method and an arrangement for measuring the concentration of gases and the pH value of a sample, e.g. blood, involving the use of a fluorescent indicator at the end of a light-conducting cable which is sealingly covered by or embedded in a selectively permeable diffusion membrane. The radiation transmitted to and emitted from the indicator must be passed through various filtering elements and light elements, including reflectors, beam splitters and amplifiers before any meaningful measurements can be made.
U.S. Pat. No. 4,041,932, Fostick, discloses a method whereby blood constituents are monitored by measuring the concentration of gases or fluids collected in an enclosed chamber sealingly attached to a skin "window" formed by removing the stratum corneum over a small area of the patient's skin. The measurements in the enclosed chamber are made, inter alia, by determining the difference in intensity of light emitted from a fluorescent indicator.
U.S. Pat. Nos. 4,200,110 and 4,476,870, Peterson et al, disclose the use of a pH sensitive indicator in conjunction with a fiber optic pH probe. In each of these patents the dye indicator is enclosed within a selectively permeable membrane envelope.
U.S. Pat. No. 4,548,907, Seitz et al, discloses a fluorescent-based optical sensor comprising a membrane immobilized fluorophor secured to one end of a bifurcated fiber optic channel for exposure to the sample to be analyzed.
Many fluorescent indicators sensitive to pH, and thereby useful for pCO.sub.2 measurements, are known in the art. Examples of useful fluorescent indicators are disclosed in the above patents and also in "Practical Fluorescence" by George E. Guilbault, (1973) pages 599-600.
Sensor devices using fluorescent indicators may be used for in vitro or in vivo determinations of components in physiological media. For in vitro determinations the size of the device is normally of no consequence, but for in vivo use, the size of the sensor may be extremely critical and there is an increasing need in the art to miniaturize sensor devices, particularly catheter-type devices, for the in vivo determination of components in physiological media, e.g. blood. However, diminution in size of the components of such devices, particularly in the size of the sensor itself, decreases the strength of the signal emitted by the indicator and consequently presents problems in the detection and measurement of said signal. These problems are aggravated when the detector system requires a multiplicity of components, such as filters, beamsplitters and reflectors to isolate and measure the emitted energy. Each of the said components reduces the emitted signal strength resulting in a sequential loss of measurable signal. Consequently, the more components present in the system, the weaker the final signal strength.
The problems associated with miniaturization of sensor devices are substantially solved by a device involving a radiation-transmissible junction of optical fibers encased in an opaque radiation reflective jacket as described and claimed in commonly assigned copending application No.
With the aid of said device the emission signal from radiation-sensitive indicators, particularly fluorescent indicators of the type disclosed in the prior art references discussed above, may be received substantially unattenuated in a suitable detector without the necessity of filters, beam splitters, reflectors or other light elements used in the prior art.
In accordance with the present invention the concept of retained signal strength embodied in the junction coupling device of the aforesaid copending application is further extended in a multi-channel system, capable of numerous modifications, for the determination of a plurality of parameters, while still retaining the advantage of optimal miniaturization without loss of signal strength.